1. Field of the Invention
The present invention relates to a switching regulator, and more specifically it relates to an isolated switching regulator.
2. Description of Related Art
Various switching regulators have been widely used for providing regulated voltage and current. For safety reasons, off-line switching regulators must provide isolation between their primary side and secondary side. Therefore, a control circuit is equipped at the primary side of a switching regulator, an optical-coupler, and the secondary-side circuit are needed to regulate an output voltage and an output current of the switching regulator. To reduce the size and cost of the switching regulator, the need of optical-coupler and secondary-side circuit to be eliminated is the trend.
In recent developments, many primary side control schemes have been disclosed such as U.S. Pat. No. 6,721,192 entitled “PWM controller regulating output voltage and output current in primary side” Yang et al., U.S. Pat. No. 6,836,415 entitled “Primary-side regulated pulse width modulation controller with improved load regulation” Yang, et al; and U.S. Pat. No. 6,862,194 entitled “Flyback power converter having a constant voltage and a constant current output under primary-side PWM control” Yang, et al. However, the drawback of the aforementioned conventional primary side control schemes is the inaccurate control of the output voltage and output current.
The object of the present invention is to provide a switching regulator that is able to accurately control the output voltage and the output current at the primary side of the switching regulator. Therefore, the size and cost of the switching regulator is reduced.